FINAL REPORT DETAILED FIELD INVESTIGATION OF VAPOR INTRUSION PROCESSES. ESTCP Project ER-0423

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1 FINAL REPORT DETAILED FIELD INVESTIGATION OF VAPOR INTRUSION PROCESSES ESTCP Project ER-0423 GSI Environmental Inc. September 2008 Distribution Statement A: Approved for Public Release, Distribution is Unlimited

2 Table of Contents Page Executive Summary E-2 1. Introduction Background Objectives of the Demonstration Regulatory Drivers Stakeholder/End-User Issues Technology Description Technology Development and Application Previous Testing of the Technology Factors Affecting Cost and Performance Advantages and Limitations of the Technology Demonstration Design Performance Objectives Selecting Test Sites Required Test Site Characteristics Preferred Test Site Characteristics Test Site Description Altus Air Force Base, Altus, Oklahoma Hill Air Force Base, Ogden, Utah Pre-Demonstration Testing and Analysis Altus Air Force Base, Altus, Oklahoma Hill Air Force Base, Ogden, Utah Testing and Evaluation Plan Demonstration Installation and Start-up Period of Operation Amount /Treatment Rate of Material to be Treated Residuals Handling Operating Parameters for the Technology Experimental Design Sampling Plan Demobilization Selection of Analytical/Testing Methods Selection of Analytical/Testing Laboratory Performance Assessment Performance Criteria 48 GSI Environmental Inc. ESTCP Project No. ER-0423 Page ii Detailed Investigation of Vapor Intrusion Processes

3 Table of Contents Page 4.2 Performance Confirmation Methods Evaluation of Data Quality Custody Procedures, Holding Time, Arrival Temperatures Sampling Procedures and Field Instrumentation Precision Assessment: Duplicate Samples, Matrix Spike and Matrix Spike Duplicate Accuracy Assessment: Blank Analysis, Laboratory Control Standards, Surrogate Recovery Completeness Assessment Responses to Identified Data Quality Issues Data Analysis, Interpretation and Evaluation Vapor Intrusion Impact Movement of VOCs Across Key Interfaces Spatial and Temporal Variability in VOC Concentrations Attenuation Factors Site Physical Characteristics Recommendations for Vapor Intrusion Sample Collection Groundwater Samples Soil Gas Samples Recommended Approach for Building-Specific Investigation of Vapor Intrusion Building-Specific Vapor Intrusion Screening Building-Specific Vapor Intrusion Evaluation Evaluation Costs Impact of Investigation Program on Attenuation Factor Accuracy Cost Assessment Cost Reporting Cost Analysis Implementation Issues Environmental Checklist Other Regulatory Issues End-User Issues References Points of Contact 105 Appendix A: Summary of Sample Point Design and Laboratory Analytical Methods Appendix B: Quality Assurance Project Plan Appendix C: Supplemental Figures for Hill AFB and Altus AFB Appendix D: Summary of Results from Third Altus AFB Event Appendix E: Example Calculations GSI Environmental Inc. ESTCP Project No. ER-0423 Page iii Detailed Investigation of Vapor Intrusion Processes

4 Table of Contents Page Appendix F: Statistical Evaluation Appendix G: Project Database of Analytical Results Appendix H: Health and Safety Plan Appendix I: Federal and State Vapor Intrusion Resources Appendix J: Response to Reviewer Comments GSI Environmental Inc. ESTCP Project No. ER-0423 Page iv Detailed Investigation of Vapor Intrusion Processes

5 Table of Contents Page List of Tables Table E.1 Table E.2 Table E.3 Table E.4 Table E.5 Table 3.1: Table : Table : Table 4.1.1: Table 4.2.1: Table 4.3.2: Table : Table : Table : Table : Table : Table : Table Table Table : Table : Table : Table : Table : Table : Table : Table : Table : Table : Table : Table : Performance Objectives Summary of Sampling Event by Demonstration Building Summary of Data Quality Performance Summary of Demonstration Performance Recommended Sample Collection Program for Evaluation of Vapor Intrusion Performance Objectives Summary of Sample Collection by Sampling Event Summary of Sample Collection and Analysis Program for a Typical Sampling Event Performance Criteria Expected Performance and Performance Confirmation Methods Data Quality Issues Associated With Sample Point Integrity Summary of Data Evaluation Results Measured Indoor and Ambient VOC Concentration: Altus AFB Measured Indoor and Ambient TCE Concentration: Hill AFB Sub-Slab to Indoor Air Attenuation Factor: Radon Sub-Slab to Indoor Air Attenuation Factor: TCE & PCE Estimated VOC Concentration in Indoor Air Due to Vapor Intrusion Average VOC to Radon Ratios Analyses Used to Evaluate Vapor Intrusion Impacts Mass Flux Along the Vapor Intrusion Pathway: Altus Demonstration Site Mass Flux Along the Vapor Intrusion Pathway: Hill Demonstration Site Evaluation of Variability in Field Duplicate Samples Spatial Variability in VOC Concentration Evaluation of Short-Term (days) Temporal Variability Evaluation of Longer-Term (months) Temporal Variability: Hill AFB Evaluation of Longer-Term (months) Temporal Variability: Altus AFB Subsurface to Indoor Air Attenuation Factors for Altus Site Demonstration Building Subsurface to Indoor Air Attenuation Factors for Hill Site Demonstration Buildings Results of Geophysical Testing Soil Permeability for Altus Site Demonstration Building Soil Permeability for Hill Site Demonstration Buildings GSI Environmental Inc. ESTCP Project No. ER-0423 Page v Detailed Investigation of Vapor Intrusion Processes

6 Table of Contents Page Table : Table : Table : Table : Table : Table : Table 5.1.1: Table 5.1.2: Table 5.2.1: Figure E.1 Figure 2.1: Photo : Photo : Photo : Photo : Photo : Photo : Figure : Figure : Evaluation of Leakage in Soil Gas Samples Recommended Typical Sample Collection Program for Evaluation of Vapor Intrusion Typical Unit Costs for Vapor Intrusion Analyses Typical Costs for Screening of a Single Family Residence Typical Costs for Evaluation of a Single Family Residence Distribution of Measured Attenuation For a Building with a True Attenuation Factor of 0.001, Assuming Log-Normal Spatial Variability Contractor and Material Costs Consultant Labor Requirements (Hours) Representative Unit Costs for Vapor Intrusion Investigation List of Figures Conceptual Data Collection Plan for Detailed Evaluation of the Vapor Intrusion Pathway Current Conceptual Model for Vapor Intrusion Soil Gas and Monitoring Well Cluster Prior to Pad Completion (Altus AFB) Indoor Soil Gas Points (Altus AFB) Sub-Slab Sample Port (Altus AFB) Soil Gas Sample Point with Sampling Apparatus Attached (Hill AFB) Cap Used for Soil Gas and Well Headspace Sampling Pressure Transducer Installed to Measure Cross-Foundation Pressure Gradient Depressurization Results: VOCs Depressurization Results: TCE and Radon Attenuation Factors GSI Environmental Inc. ESTCP Project No. ER-0423 Page vi Detailed Investigation of Vapor Intrusion Processes

7 List of Acronyms AFB AFCEE API BTEX bgs COC CSM 1,1-DCE DoD DQO ECD EPA ESTCP FID GC GC/MS HVAC LCS MCL MDL MQL MS/MSD MTBE NAPL NELAP O&M OSHA OSWER Ppbv PCE PID PVC QA/QC QAPP RBCA RCRA RL RPD SF 6 SIM SOP SVOC TCA List of Acronyms Air Force Base Air Force Center for Environmental Excellence American Petroleum Institute benzene, toluene, Ethylbenzene, and xylenes below ground surface chemical of concern conceptual site model 1,1-dichloroethene Department of Defense data quality objective electron capture detector Environmental Protection Agency Environmental Strategic Technology Certification Program flame ionization detector gas chromatography gas chromatography/mass spectrometry heating, ventilation, air conditioning laboratory control standard maximum concentration level method detection limit method quantitation limit matrix spike/matrix spike duplicate methyl tertiary-butyl ether non-aqueous phase liquid National Environmental Laboratory Accreditation Program operation and maintenance Occupational Safety and Health Administration Office of Solid Waste Emergency Response parts per billion by volume tetrachloroethene (also called perchloroethene) photoionization detector polyvinyl chloride quality assurance/quality control Quality Assurance Project Plan risk-based corrective action Resource Conservation and Recovery Act reporting limit relative percent difference sulfur hexafluoride selective ion monitoring standard operating procedure semivolatile organic compound trichloroethane GSI Environmental Inc. ESTCP Project No. ER-0423 Page vii Detailed Investigation of Vapor Intrusion Processes

8 List of Acronyms TCE TCEQ TPH VI VOC trichloroethene Texas Commission on Environmental Quality total petroleum hydrocarbons vapor intrusion volatile organic compound GSI Environmental Inc. ESTCP Project No. ER-0423 Page viii Detailed Investigation of Vapor Intrusion Processes

9 Acknowledgements This project would not have been possible without the support and contribution of numerous individuals and organizations. The authors thank Ivette O Brien and Samuel Brock of Air Force Center for Environmental Excellence (AFCEE) for support and oversight; Kyle Gorder, Art Whallon, Charles Butchee, and other personnel at Hill Air Force Base (AFB) and Altus AFB for providing access and facilitating implementation of the project at these bases; Blayne Hartman and the staff of H&P Mobile Geochemistry for project support; Doug Hammond of the University of Southern California for analysis of radon concentrations in air and soil gas samples; Chet Clarke of the Texas Commission on Environmental Quality (TCEQ) for review and comment on the project plan; the ESTCP technical review staff for helpful technical comments and suggestions; and Andrea Leeson and the Environmental Strategic Technology Certification Program (ESTCP) program staff at Hydrogeologic for invaluable project support. GSI Environmental Inc. ESTCP Project No. ER-0423 Page E-1 Detailed Investigation of Vapor Intrusion Processes

10 Executive Summary Demonstration Objectives The primary objective of this demonstration study was to identify a cost effective and accurate protocol for investigation of vapor intrusion into buildings overlying contaminated groundwater. Performance objectives are summarized in Table E.1. Table E.1: Performance Objectives Primary Performance Criteria Type of Performance Objective Quantitative Quantitative Qualitative 1) Collection of data representative of site conditions. 2) Vapor Intrusion Impact at Demonstration Site 3) Reliable Vapor Intrusion Investigation Approach Expected Performance (Metric) Precision, Accuracy, Completeness, Representativeness, and Comparability as defined in Table and Appendix B. Indoor air concentration of COC above risk-based screening limit and not attributable to background indoor air sources. Accuracy of vapor intrusion determination as characterized by false positive and false negative rates. Identify limited scope investigation approach with higher accuracy than current approaches such as USEPA Actual Performance Objective Met? Objective Attained (See Section 4.3) Objective Attained (See Section 4.4.1) Objective Attained (See Section 4.6) Intensively monitored sites, such as the Borden Landfill in Canada, have greatly contributed to our understanding of the physical and chemical processes that control the transport of chemicals in groundwater. For this project, we have used a similar approach (i.e., intensively monitored sites with specially-designed monitoring networks) to address the critical groundwater-to-indoorair vapor intrusion pathway. The performance objectives were met by: 1) Collecting a high density of data related to vapor intrusion at the test sites, 2) Analyzing this data to obtain a thorough understanding of vapor intrusion processes at the test sites, and 3) Utilizing the results to develop a reliable and cost-effective approach for investigation of vapor intrusion at other sites. Regulatory Drivers At a limited number of sites in the U.S., migration of volatile organic compounds (VOC) from affected groundwater via vapor phase diffusion has impacted indoor air quality in overlying structures, posing a potentially significant, yet previously unrecognized human health concern for such properties. To address this concern, the Environmental Protection Agency (EPA) has GSI Environmental Inc. ESTCP Project No. ER-0423 Page E-2 Detailed Investigation of Vapor Intrusion Processes

11 issued the Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils, (EPA 2002), providing conservative screening limit concentrations for various VOC in groundwater. The high level of conservatism in the EPA and state guidance reflects the current limitations of our understanding of the physical and chemical processes that contribute to vapor intrusion. A primary goal of this project has been to support the development of refined vapor intrusion guidance based on an improved understanding of the site-specific factors which influence vapor intrusion. Overview of Demonstration For this demonstration, vapor intrusion site investigations have been completed at a total of three buildings located at two demonstrations sites: two single-family residences near Hill AFB and a small office building at Altus AFB. For each site, the investigation program consisted of an initial sample point installation and sampling event and one (Hill AFB) or two (Altus AFB) follow-up sampling events. The sampling program, illustrated in Figure E.1, was designed to yield a high density of data around each of the demonstration buildings. Figure E.1 Conceptual Data Collection Plan for Detailed Evaluation of the Vapor Intrusion Pathway: 1) Multi-level Discrete Depth Samples Upgradient, Midgradient, and Downgradient of the Building Used to Characterize Groundwater Mass Flux (3 multi-level clusters); 2) Multi-level Soil Gas Sampling Conducted Below or Adjacent to the Building used to Characterize Soil Gas Concentration Gradients and Mass Flux (3 multi-level clusters); 3) Sub-slab Soil Gas Samples, Combined with the other Data, Provide an Understanding of Transport From the Groundwater Source to Indoor Air (3 sample points); 4) Indoor Air Samples (3 sample points), Combined with 5) Ambient Air Samples (3 sample points) and 6) Analysis of Radon Allows Separation of Indoor Air Sources and Vapor Intrusions Sources; 7) Unique Tracer Gas Released Within the Building Allows for Accurate Measurement of Building Air Exchange Rate. GSI Environmental Inc. ESTCP Project No. ER-0423 Page E-3 Detailed Investigation of Vapor Intrusion Processes

12 In order to fully characterize the distribution of VOCs at each site, several sampling events were conducted at each building as summarized in Table E.2. Table E.2: Summary of Sampling Event by Demonstration Building. Demonstration Building Sample Event Altus 418 Hill Res. #1 Hill Res. #2 Soil Gas Point Purge Study X X X Initial Sampling Event X X X Short-Term Follow-up X Longer-Term Follow-up X (2 events) X X Building Depressurization X This sampling program yielded a large data set suitable for detailed evaluation of vapor intrusion processes. Summary of Data Quality The collection of site data representative of actual site conditions was achieved through compliance with the Quality Assurance Project Plan (QAPP), included as Appendix B. The QAPP details the sampling and analysis procedures that were utilized for each type of sample collected during the data collection portion of the project. In addition, the QAPP defines quality assurance objectives for precision, accuracy, completeness, representativeness, and comparability that were used to quantitatively evaluate the quality of the data obtained. For the purpose of the data usability evaluation, analytical results were evaluated in groups: i) custody procedures, holding time, arrival temperatures, ii) sampling procedures and field instrumentation, iii) precision assessment, iv) accuracy assessment, and v) completeness assessment. A summary data usability evaluation for this project is presented in Table E.3. GSI Environmental Inc. ESTCP Project No. ER-0423 Page E-4 Detailed Investigation of Vapor Intrusion Processes

13 Table E.3: Summary of Data Quality Performance. Performance Criteria Expected Performance Metric Performance Confirmation Method Performance Criteria for Data Quality Assurance (Quantitative) +/- 30% relative percent 1 duplicate per 20 Precision difference (RPD) samples for all VOC, SF 6, and radon analyses Accuracy Completeness Field blanks below PQLs. Laboratory accuracy as defined in Appendix B, Tables 2.2 and 2.3 > 90% valid field samples. >95% valid laboratory results (water and air/gas) All VOC analyses (water and air/gas) All VOC analyses (water and air/gas) Performance Criteria for Data Quality Assurance (Qualitative) Use of field sampling procedures, laboratory Representativeness analytical procedures, sample holding times, etc. defined in QAPP Comparability Use of standard and consistent sampling and analysis procedures for all samples, as defined in QAPP Actual (Post Demo) RPD goal met in 82% of duplicate pairs Goal achieved in 98% of field blanks and laboratory QA/QC samples Achieved All field samples Goal achieved for 99% of samples All field samples Goal achieved for 99% of samples Over the course of the project, we implemented changes to field procedures to address minor data quality issues identified from previous events. To the extent possible, consistent field procedures were used across sampling events to ensure comparable results were obtained. The resulting project data set was determined to be suitable for evaluation of vapor intrusion in accordance with the defined performance objectives. GSI Environmental Inc. ESTCP Project No. ER-0423 Page E-5 Detailed Investigation of Vapor Intrusion Processes

14 Summary of Demonstration Findings The demonstration data set was evaluated in accordance with the performance criteria defined in the project demonstration plan and summarized in Table E.4. Table E.4: Summary of Demonstration Performance Expected Performance Performance Actual Performance Criteria Metric Confirmation Method (Post Demo) Performance Criteria for Technology Demonstration (Qualitative and Quantitative) Presence or absence of vapor intrusion impact at test site. Vapor intrusion impact defined as indoor air concentration of COC above risk-based screening limit and not attributable to background indoor air Vapor Intrusion Impact sources Movement of VOCs Across Key Interfaces Calculation of mass flux across key vapor intrusion pathway interfaces, see Section 4.3 of Demonstration Plan Detection of VOCs in indoor air at concentrations exceeding USEPA, 2002 indoor air screening limits. If limits exceeded, evaluation of sub-slab and indoor air data to separate vapor intrusion from background indoor air sources as described in Section 4.3 of Demonstration Plan Consistent or decreasing mass flux along the vapor intrusion pathway Evaluation of indoor, ambient, and sub-slab VOC and radon concentrations indicated an absence of vapor intrusion impacts above applicable regulatory limits in all three of the demonstration buildings during each of the sampling events. Application of the same investigation approach at other buildings would be expected to yield definitive results concerning the presence or absence of a vapor intrusion impact (see Section 4.4.1) Calculated mass flux values had high uncertainty and did not show a consistently decreasing mass flux along the vapor intrusion pathway (See Section 4.4.2) GSI Environmental Inc. ESTCP Project No. ER-0423 Page E-6 Detailed Investigation of Vapor Intrusion Processes

15 Performance Criteria Spatial and Temporal Variability in VOC Concentration Attenuation Factors Site Physical Characteristics Reliable Vapor Intrusion Investigation Approach Expected Performance Metric Calculation of spatial and temporal variability in chemical concentration for each environmental medium investigated Calculation of attenuation factors describing the attenuation of chemicals from various environmental media to indoor air Measurement of site soil characteristics and other physical characteristics of the site Identification of a limited site investigation program that will provide a reliable indication of vapor intrusion impacts Performance Confirmation Method Statistical measures of variability as described in Section 4.3 of Demonstration Plan Statistical measures of variability as described in Section 4.3 of the Demonstration Plan Correlation of site characteristics to VOC distributions and fluxes as described in Section 4.3 of the Demonstration Plan Statistical comparison of accuracy of vapor intrusion impact predicted by limited subset of site data compared to full set of data obtained for the site, as described in Section 4.3 of the Demonstration Plan Actual (Post Demo) High spatial and longerterm (months) temporal variability in subsurface VOC concentrations compared to aboveground VOC concentrations indicate that a larger number of samples are required to characterize VOC concentrations in subsurface media. Analytical, sample, and short-term (days) temporal variability do not appear to be a major sources of uncertainty in vapor intrusion evaluations (see Section 4.4.3) Calculated attenuation factors had moderate to high uncertainty but were consistently below USEPA default values for pathway screening See Section 4.4.4) Data set did not show expected correlation between lower soil permeability and higher VOC attenuation (See Section 4.4.5) We have developed a recommended approach for the reliable investigation of vapor intrusion. (See Section 4.6) GSI Environmental Inc. ESTCP Project No. ER-0423 Page E-7 Detailed Investigation of Vapor Intrusion Processes

16 Key project findings are summarized as follows: Vapor Intrusion Impact: A vapor intrusion impact, defined as an exceedance of applicable indoor air VOC concentration screening values attributable to vapor intrusion, was not observed in any of the demonstration buildings. However, a statistically significant increase in indoor VOC concentration relative to ambient concentrations was observed during some sample events. The analysis of VOC and radon concentrations in ambient air, indoor air, and sub-slab gas samples, provided a data set that could be used to identify the most likely source of VOC detected in indoor air. This analysis indicated that trichloroethene (TCE) in indoor air during the second Altus sampling event at concentrations above EPA screening levels were attributable to ambient sources and not vapor intrusion. The data evaluation indicated some migration of TCE and/or PCE from the subsurface to indoor air at the demonstration buildings during some sample events, however, in all cases the estimated VOC concentration in indoor air attributable to vapor intrusion was below the applicable screening level for the site. The impact of induced building depressurization on vapor intrusion (VI) was evaluated at Hill AFB Residence #1 and the results indicate that this may be a useful tool for the evaluation of vapor intrusion under worst case conditions. However, further validation of this approach is needed. Use of Radon as a Tracer for Soil Gas Movement into Buildings: Based on the difference between indoor and ambient radon concentrations and the absence of indoor sources of radon, radon was determined to be a sensitive tracer for the movement of soil gas through the building foundation. The measured radon attenuation factors have been used to calculate the concentration of VOCs in indoor air attributable to vapor intrusion and to evaluate the possible contribution of indoor VOC sources to measured indoor VOC concentrations. For example, the difference between the measured concentration of TCE indoor air and the estimated concentration attributable to vapor intrusion suggested a likely indoor source of TCE at Altus AFB Building 418 in December 2006 and at Hill AFB Residence #1 in March 2006 (see Table ). Radon is a useful tracer for the movement of soil gas because radon is emitted from all soils and is present in all soil gas. However, because VOCs in soil gas originate from specific sources while radon in soil gas originates from all soils, the distribution of radon and VOC may be different within subsurface gas below a building. This difference could result in differences between the measured attenuation factors that are not attributable to indoor sources of VOC. Radon data is likely to be most useful for the evaluation of vapor intrusion when radon and VOC concentrations are measured at multiple sub-slab sample locations allowing for an evaluation of the differences in subsurface distribution of these chemicals. Movement of VOCs Across Key Interfaces: Mass flux was used to track the movement of VOC across key interfaces along the vapor intrusion pathway. Mass flux through shallow groundwater was consistently higher than mass flux through soil gas or through the building foundation indicating that only a small fraction of the VOC mass diffused from groundwater to soil gas as GSI Environmental Inc. ESTCP Project No. ER-0423 Page E-8 Detailed Investigation of Vapor Intrusion Processes

17 the groundwater migrated under the demonstration building. In contrast, no consistent relationship was observed between estimated mass flux through soil gas and through the building foundation. The large uncertainty in mass flux estimates may limit their utility for evaluation of vapor intrusion. The accuracy of the mass flux estimate is limited by both spatial variability in VOC concentration and uncertainty in site hydrogeologic parameters required for the mass flux calculations. Because the lateral mass flux of VOC through shallow groundwater below a building is typically higher than the vertical mass flux of VOC through the soil column below the building, evaluation of mass flux in shallow groundwater may provide a conservative screening tool for the vapor intrusion pathway when this mass flux is less than would be required to sustain an indoor vapor intrusion impact. However, further validation of the utility of groundwater mass flux for screening of vapor intrusion would be required. Spatial and Temporal Variability in VOC Concentration: Demonstration results were analyzed to determine the most important sources of variability in VOC concentrations during vapor intrusion investigations. Relative percent difference (RPD) was used to describe variability between paired measurements and coefficient of variation (CV) was used to describe variability in data sets of three or more measurements. Analytical variability was very low with an average RPD between laboratory duplicate measurements of 2.5% and surrogate recoveries typically between 98% and 102%. Field duplicate variability was higher, but acceptable, with 78% of field duplicate VOC measurements (and 82% of all field duplicate measurements) achieving the data quality objective of an RPD<30%. Short-term temporal variability (i.e., time scale of days) was only slightly higher than field duplicate variability with 65% of duplicate VOC measurements showing an RPD<30%. These results indicate the variability on the time scale of days was largely influenced by sample collection and/or very small-scale field variability. Spatial variability in VOC concentration was evaluated through the CV in VOC concentrations between samples from three spatially-separated sample points. Spatial variability was much higher in subsurface gas samples (i.e., average CV = 0.92 to 0.96 in sub-slab, soil gas, and well headspace samples) compared to indoor (average CV = 0.26) and ambient air samples (average CV = 0.55). Based on this finding, an efficient vapor intrusion investigation program that includes samples from both media should include a larger number of subsurface gas samples than above-ground air samples. Longer-term temporal variability (i.e., time scale of months) in subsurface gas samples was similar to the spatial variability (i.e., average CV = 0.80 to 1.02 in sub-slab, soil gas, and well headspace samples). This finding suggests that subsurface gas sampling should be balanced between spatially separated sample points and temporally separated sample events. Attenuation Factors: There was significant uncertainty in the calculated subsurface to indoor air attenuation factors, with the standard deviation for the calculated values similar to or greater than the calculated attenuation factor values. Despite this uncertainty, the calculated attenuation factors were consistently less than the EPA default values indicating that the EPA default values GSI Environmental Inc. ESTCP Project No. ER-0423 Page E-9 Detailed Investigation of Vapor Intrusion Processes

18 were conservative and protective for the three demonstration buildings evaluated. Measured sub-slab to indoor air attenuation factors ranged from 3.8 x 10-4 to 7.6 x 10-3 compared to the current EPA default value of 1.0 x 10-1 and the proposed value of 5.0 x Measured groundwater to indoor air attenuation factors ranged from 2.9 x 10-6 to 3.6 x 10-4 compared to the current EPA default value of 1.0 x 10-3 (the USEPA has not proposed to change this default value). Typically, attenuation factors are calculated based a single subsurface and a single indoor air measurement. For this project, each attenuation factor was calculated based on a minimum of three subsurface and three indoor air measurements. The high uncertainty associated with these relatively data rich attenuation factors indicates that typical attenuation factors are extremely uncertain and may have limited utility for evaluation of the vapor intrusion pathway. Site Physical Characteristics: The demonstration yielded a limited data set for the evaluation of site physical characteristics, supporting only a limited evaluation of the impact of site characteristics on vapor intrusion. However, the available data do not support the hypothesis that lower permeability vadose zone soils decrease the potential for vertical migration of VOCs from groundwater through the unsaturated soil column, decreasing the potential for vapor intrusion impacts. At the Hill AFB site, the vadose zone soil permeability was approximately 10x higher at Residence #2 compared to Residence #1 based on both laboratory and field measurements. However, the March 2006 sampling event indicated vertical migration of TCE through the vadose zone soils to the building at Residence #1 but not at Residence #2 despite similar concentration of TCE measured in shallow groundwater at the top of the water table at the two residences. As a result, the groundwater to indoor air attenuation factor at Residence #1 was at least 50x higher than at Residence #2, where non-detect results for TCE in sub-slab samples yielded an upper-bound estimate of the attenuation factor. These results indicate greater VOC attenuation at Residence #2, despite the presence of higher permeability vadose zone soils at this location. (Note that a higher value for the attenuation factor indicates less VOC attenuation). Recommendations for Investigation of Vapor Intrusion: The results of the demonstration have been used to develop a recommended sample collection program for the evaluation of vapor intrusion in individual buildings, summarized in Table E.5. GSI Environmental Inc. ESTCP Project No. ER-0423 Page E-10 Detailed Investigation of Vapor Intrusion Processes

19 Table E.5: Recommended Sample Collection Program for Evaluation of Vapor Intrusion. Environmental Medium Analyses Sample Duration Sample Container Number of Samples Sample Locations Ambient air VOCs by TO hr 6L Summa 1 Upwind Radon 2 Grab 0.5 L Tedlar 1 Indoor air VOCs by TO hr 6L Summa Lowest floor Radon 2 Grab 0.5 L Tedlar Sub-slab gas VOCs by TO-15 Radon 2 Grab Grab 0.4L or 1L Summa 0.5 L Tedlar Distributed below lowest floor * Note: 1) TO-15 SIM may be required for indoor and ambient air samples to achieve detection limits below regulatory screening values. TO-15 analyses are conducted by numerous commercial laboratories. The TO-15 analyte list may vary between laboratories and should be reviewed to ensure inclusion of all volatile COC. 2) Radon samples analyzed by Dr. Doug Hammond (dhammond@usc.edu) at the University of Southern California Department of Earth Sciences using the extraction method of Berelson, 1987 and the analysis method of Mathieu, ) Recommended number of samples for a typical residence with a ft 2 foundation. Additional samples may be appropriate for larger structures. The results of the investigation program should be used to evaluate vapor intrusion based on a weight-of-evidence approach using the following data evaluation methods: Indoor Air Data: If indoor VOC concentrations are below indoor screening levels then no further immediate evaluation of vapor intrusion is required. Additional follow-up monitoring may be warranted at some buildings to evaluate the potential for intermittent vapor intrusion impacts to occur at other times. Evaluation of Potential VOC Sources: If indoor VOC concentrations exceed indoor screening levels, then VOC and radon concentrations should be evaluated to help identify the most likely source or sources of the indoor air impacts. Evidence of Ambient Sources: Ambient VOC concentrations greater than or similar to indoor VOC concentrations indicate that ambient sources are the likely primary source of VOCs in indoor air. Evidence of Indoor Sources: Indoor VOC concentrations >10% of below foundation concentrations, and/or large differences in below foundation to indoor air attenuation factors between VOC, indicate that indoor sources are likely the primary source of one or more of the VOC in indoor air. For example, a tetrachloroethene (PCE) attenuation factor of 0.03 and a TCE attenuation factor of would suggest a likely indoor source of PCE. Evidence of Vapor Intrusion: The following factors together indicate that vapor intrusion is likely the primary source of observed indoor air impacts: i) indoor VOC concentrations greater than ambient VOC concentrations, ii) below foundation to indoor air attenuation factors <0.01 and, iii) below foundation to indoor air attenuation factors similar for all VOCs and for radon. GSI Environmental Inc. ESTCP Project No. ER-0423 Page E-11 Detailed Investigation of Vapor Intrusion Processes

20 Currently available regulatory guidance does not provide clear and consistent recommendations for the field evaluation of VI at individual buildings. As a result, the current approaches to the investigation of VI vary widely between sites. When comparing investigation results between sites, it is difficult to separate the effects of site characteristics from the effects of differing investigation methods. The application of a consistent field investigation program, such as that recommended here, across buildings and sites will yield comparable data sets that provide an improved understanding of the site-specific factors contributing to the presence or absence of vapor intrusion impacts at individual buildings. Typical costs for the recommended investigation approach are provided in Section of this report. Summary of Project Deliverables The results of this demonstration have been used to generate the following products: 1) Procedural Guidelines for Reliable Evaluation of Vapor Intrusion: A cost-effective and reliable approach for the evaluation of vapor intrusion. Provided as a white paper, Recommendations for the Investigation of Vapor Intrusion and also presented in Section 4.6 of this report. 2) Accessible Site Characterization Database: A web-accessible database presenting the data collected for this project. This database provides VOC concentration results as well as other site characteristics such as soil parameters and building characteristics. It provides an empirical dataset for evaluation of predictive vapor intrusion models. In addition, the database allows other interested parties to evaluate spatial and temporal variability of VOC in groundwater, soil gas, sub-slab gas, and indoor air. 3) Technology Transfer: A fact sheet and several peer-reviewed publications present key findings that are likely to be useful to state and federal regulators, and others, responsible for establishing policies related to vapor intrusion. 4) Permanent and Reusable Monitoring Systems: The monitoring networks installed at the two sites selected for this study have been constructed so as to facilitate future resampling and reuse as desired by Department of Defense (DoD). Similar to the Borden Landfill approach, these facilities can be used in future studies to accommodate the continued development and validation of an improved conceptual model and predictive tools for the vapor intrusion pathway. GSI Environmental Inc. ESTCP Project No. ER-0423 Page E-12 Detailed Investigation of Vapor Intrusion Processes

21 DETAILED FIELD INVESTIGATION OF VAPOR INTRUSION PROCESSES 1. Introduction 1.1 Background Problem: Although the scientific and regulatory communities have been aware of the subsurfaceto-indoor air VI pathway for over two decades, most of the early focus regarding this pathway was limited to the migration of radon or landfill gas into indoor air (Altshuler and Burmaster 1997; Richardson 1997; Folkes and Arell 2003). In the early nineties, this pathway drew renewed interest from the regulatory community due to the implementation of risk-based corrective action (RBCA) concepts (ASTM 1994) at corrective action sites, and due to the publication of the Johnson-Ettinger Model (Johnson and Ettinger 1991). The Johnson-Ettinger model extended some of the assumptions employed originally in radon vapor intrusion models to represent diffusive and pressure-driven (i.e., advective) transport of volatile organic compounds (VOC) from a subsurface vapor source to indoor air. In the mid-nineties, several state regulatory agencies and the EPA (EPA 2000) applied the Johnson-Ettinger model, together with conservative assumptions, to develop risk-based groundwater screening levels that would be protective of human exposure to indoor air impacted by VI. In the late 1990s, the groundwaterto-indoor air vapor intrusion pathway received national attention when two Colorado sites with chlorinated solvent groundwater plumes were found to have elevated levels of chlorinated VOC in the indoor air of overlying surface structures (Renner, 2002). Largely in response to the findings at the two Colorado sites, the Corrective Action Branch of the Office of Solid Waste and Emergency Response (OSWER) at the EPA developed and released a draft supplemental guidance in 2001 (EPA 2001) to facilitate the evaluation of VI at RCRA corrective action facilities. In November 2002, the EPA issued the Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils ( EPA Vapor Intrusion Guidance ; (EPA 2002), to extend the evaluation of the VI pathway to Superfund and other corrective action sites (Folkes and Arell 2003). Due to the failure of modeling to identify the vapor intrusion impacts at the Colorado sites, these EPA draft guidance documents have a reduced reliance on models for pathway screening and have increased the requirements for direct measurement to evaluate the potential for vapor intrusion at corrective action sites. In addition, a number of state and local regulatory agencies have recently issued new or updated guidance that similarly emphasizes field measurements over modeling for the evaluation of VI (WDHFS 2003; PaDEP 2004; NJDEP 2006; NYDOH 2006). The EPA and state guidance documents use conservative screening procedures to compensate for a limited understanding of the site-specific parameters that control the VI processes. An improved understanding of these processes at sites with VOC contamination will support the development of improved site investigation approaches and refined regulatory guidance. Technology Demonstration: Intensively monitored sites, such as the Borden Landfill in Canada, have greatly contributed to our understanding of the physical and chemical processes that control the transport of chemicals in groundwater. For this project, we have used a similar approach GSI Environmental Inc. ESTCP Project No. ER-0423 Detailed Investigation of Vapor Intrusion Processes

22 (i.e., intensively monitored sites with specially-designed monitoring networks) to address the critical groundwater-to-indoor-air vapor intrusion pathway. By increasing our understanding of this critical pathway, guidelines can be improved, thereby better focusing efforts and associated cost increases on only those sites where indoor vapor concerns are warranted. Towards this end, this project has focused on validating a streamlined site investigation technology by obtaining a detailed understanding of vapor intrusion processes associated with dissolved chlorinated solvent plumes at Altus Air Force Base (Altus AFB) in Oklahoma and Hill Air Force Base (Hill AFB) in Utah. This technology will reduce site investigation costs associated with vapor intrusion at DoD facilities by reducing the amount of data required to evaluate vapor intrusion and by increasing the accuracy of the evaluation. 1.2 Objectives of the Demonstration Objectives: The primary objective of this demonstration study was to identify a cost effective and accurate protocol for investigation of VI into buildings overlying contaminated groundwater. This objective was met by: 1) Collecting a high density of data related to vapor intrusion at the test sites, 2) Analyzing this data to obtain a thorough understanding of VI processes at the test sites, and 3) Utilizing the results to develop a reliable and cost-effective approach for the investigation of vapor intrusion at other sites. In this report, the term vapor intrusion impact is used to describe the presence of a vapor intrusion condition that requires a response action due to an exceedance of applicable regulatory screening levels. The meaning of the term vapor intrusion impact is intended to be similar to the terms soil impact or groundwater impact which are commonly used to describe exceedances of regulatory standards at corrective action sites. For this purpose, a vapor intrusion impact is defined as the presence of VOC, or other volatile chemicals, attributable to vapor intrusion in a building at concentrations requiring a response action. The indoor VOC concentration requiring a response action is typically established by the applicable regulatory authority and may be based on considerations of risk, background, and/or analytical detection limits. Although risk-based concentrations are typically based on chronic exposure, many regulatory authorities require a response action to address any measured exceedances of these concentrations including shortterm exceedances. Because COC in indoor air may originate from sources other than vapor intrusion, the detection of COC in indoor air at concentrations above a regulatory standard is not sufficient to define a VI impact in all cases. For this report, VI impacts at the demonstration sites have been evaluated in the context of both EPA vapor intrusion guidance (EPA 2002) and the regulatory standards applicable to the individual demonstration sites. In order to support the primary objective, the following specific data evaluation objectives were established: GSI Environmental Inc. ESTCP Project No. ER-0423 Detailed Investigation of Vapor Intrusion Processes

23 1) Characterize the Distribution of VOC Within Environmental Media: Characterize the spatial variability in VOC distribution within specific environmental media. Describe the differences in variability between media. Sample on multiple dates to define both shortterm variability (time scale of days) and longer-term variability (time scale of months) in VOC distribution at the demonstration site. 2) Measure VOC Transfer at Saturated/Unsaturated Zone Interface and Throughout Vapor Migration Pathway: Obtain detailed information regarding the mass flux of VOC: i) with depth within the groundwater unit, ii) vertically within the unsaturated soil column, and iii) through the building foundation. 3) Characterize Measurable Site Parameters Related to Vapor Migration Potential: Sample and analyze soils in saturated and unsaturated soil zones and evaluate building characteristics to understand physical parameters that may control potential for and rate of vapor migration including: soil lithology, depth to groundwater, height of capillary fringe, soil hydraulic conductivity and air permeability, soil water retention characteristics, vertical distribution of volumetric moisture content in unsaturated zone, soil organic carbon content, groundwater flow gradient, indoor air exchange rate, building differential pressure, etc. 4) Characterize Vapor Intrusion Mechanisms and Drivers: Conduct detailed analysis of site database to characterize groundwater to vapor transport mechanisms (diffusion in groundwater, groundwater to vapor transfer, vapor diffusion, vapor-structure interaction, VOC mass balance, temporal variation, etc.) and the importance of key site parameters (groundwater concentration, groundwater mass flux, capillary height, soil moisture profile, soil permeability, etc.) to vapor mass flux into the structure. 5) Characterization of Temporal Variability: Collect and analyze multiple samples from fixed sample points to evaluate temporal variability in VOC mass distribution on the time scales of days and months. If possible, correlate changes in mass distribution to seasonal variations in site characteristics such as ambient temperature and seasonal changes in water table elevation. 6) Characterization of Spatial Variability: Collect and analyze samples from closely-spaced sample points to evaluate the significance of spatial variability around individual buildings (i.e., on the scale of 10s of feet). Collect and analyze samples over multiple sample events to evaluate temporal changes in this spatial variability. Understanding the sources of variability in vapor intrusion data is important for designing VI investigations that maximize the value of information collected with limited resources. For example, if spatial variability is more important than temporal variability then the investigation program would be designed with more sample points but fewer sample events. Scope of Demonstration: For this demonstration, vapor intrusion site investigations have been completed at a total of three buildings located at two demonstrations sites: two single-family residences near Hill AFB, and a small office building at Altus AFB. At each site, the GSI Environmental Inc. ESTCP Project No. ER-0423 Detailed Investigation of Vapor Intrusion Processes

24 investigation program consisted of an initial sample point installation and sampling event and one (Hill AFB) or two (Altus AFB) follow-up sampling events. The sampling program was designed to yield a high density of data around each of the demonstration buildings. Project Results: The results of this demonstration have been used to generate the following products: 1) Procedural Guidelines for Reliable Evaluation of Vapor Intrusion: A cost-effective and reliable approach for the evaluation of VI. Provided as a White Paper, Recommendations for the Investigation of Vapor Intrusion. 2) Accessible Site Characterization Database: A web-accessible database presenting the data collected for this project. This database provides VOC concentration results as wells as other site characteristics such as soil parameters and building characteristics. It provides an empirical dataset for evaluation of predictive vapor intrusion models. In addition, the database allows other interested parties to evaluate spatial and temporal variability of VOC in groundwater, soil gas, sub-slab gas, and indoor air. 3) Technology Transfer: A fact sheet and several peer-reviewed publications present key findings that are likely to be useful to state and federal regulators and others responsible for establishing policies related to VI. 4) Permanent and Reusable Monitoring Systems: The monitoring networks installed at the two sites selected for this study have been constructed so as to facilitate future resampling and reuse as desired by DoD. Similar to the Borden Landfill approach, these facilities can be used in future studies to accommodate the continued development and validation of an improved conceptual model and predictive tools for the VI pathway. 1.3 Regulatory Drivers At a limited number of sites in the U.S., migration of VOC from affected groundwater via vapor phase diffusion has impacted indoor air quality in overlying structures, posing a potentially significant, yet previously unrecognized, human health concern for such properties. The EPA s solid and hazardous waste program established by the Resource Conservation and Recovery Act (RCRA) and the Superfund program established by CERCLA, both utilized risk assessment to determine the need for cleanup of waste sites (EPA 2007). In addition, the Occupation Safety and Health Administration (OSHA) and DoD policy require the maintenance of a safe work environment (US_Air_Force 1993; OSHA 2007). As a result, the potential for vapor intrusion to indoor air must be evaluated at sites with volatile chemicals present in soil or groundwater underlying occupied buildings. To address this concern, the EPA has issued the Draft Guidance for Evaluating the Vapor Intrusion to Indoor Air Pathway from Groundwater and Soils, (EPA 2002), providing conservative screening limit concentrations for various VOC in groundwater. The high level of conservatism in the EPA and state guidance reflects the current limitations in our understanding of the physical and chemical processes that contribute to VI. A primary goal of this project has been to support the development of refined vapor intrusion guidance based on an improved understanding of the site-specific factors that influence VI. GSI Environmental Inc. ESTCP Project No. ER-0423 Detailed Investigation of Vapor Intrusion Processes